Imaging apparatus with a motor component

ABSTRACT

According to one aspect of the present invention, an imaging apparatus includes an annular motor with a central opening and a plurality of lens elements positioned inside the central opening. The motor includes a stator and a homogeneous cylindrical rotor. This rotor is positioned inside the stator and is 0.5 mm to 1.5 mm thick and 2.5 mm to 5 mm long. According to one embodiment of the present invention the rotor is characterized by an outer cylindrical surface defined by its circumference. The rotor has a plurality of magnetic poles, and the ratio of the circumference of the outer cylindrical surface to the number of magnetic poles is between 1 and 2.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the following applications filed concurrently herewith: Ser. No. 09/207,737, filed Dec. 8, 1998 and entitled "An Aperture/Shutter System and A Stepper Motor for Use Therein" by Jean F. Depatie et al; and Ser. No. 09/207,727, filed Dec. 8, 1998 and entitled "Aperature/Shutter System with a Motor Component" by Jean F. Depatie et al.

FIELD OF THE INVENTION

The present invention relates in general to an imaging apparatus, such as a camera, utilizing a motorized aperture and/or shutter system.

BACKGROUND OF THE INVENTION

An imaging apparatus, such as a typical photographic camera, includes a lens barrel assembly comprising at least one barrel supporting one or more lens elements and a shutter assembly. Such a shutter assembly 5 is illustrated in FIG. 1. The shutter assembly 5 includes a ring 20 and several blades 10a, 10b, 10c that open by a variable amount to provide the desired aperture for the proper exposure. The shutter assembly is enclosed by the two housing parts 18A and 18B. The movement of the blades is controlled by a pinion gear 22 of a stepper motor 24 via use of the ring 20. The motor 24 and the pinion gear 22 are located external with respect to the shutter assembly. The ring 20 includes a sector gear with a plurality of gear teeth 20b that engages the teeth of the pinion gear 22. Thus, when the rotor 24a of the stepper motor 24 rotates, the pinion gear 22 attached to the stepper motor 24 also rotates, rotating the ring 20. The ring 20 includes posts 20a which are coupled to the slots 10a', 10b', 10c' in each of the blades 10a, 10b, 10c. The rotation of the ring 20 moves the blades, changing the size of the aperture. The blades 10a, 10b, 10c are moved in a series of steps from the closed position to achieve the desired aperture size, stay in this position for the desired exposure time and then reverse into the closed position. This configuration results in multiple parts, complex assembly and the expense due to precision alignment of the stepper motor to the shutter assembly, and the alignment of the gear teeth of the pinion gear to the poles of the stepper motor 24.

In addition, the shutter assembly is a separate part from the lens barrel assembly. Thus, the shutter assembly and the lens barrel assembly need to be precision aligned with respect to one another. This type of alignment is difficult, expensive and produces an incorrect exposure if the alignment is not performed properly. Finally, this configuration results in a large package size.

U.S. Pat. No. 4,005,448 discloses a programmable shutter and uses a stepper motor to control its position. The patent describes construction of the stepper motor for shutter actuator control and a control circuit for supplying the pulses to the stepper motor and aperture/shutter driver control circuit. More specifically, FIG. 4 of this patent illustrates that the motor comprises a stator and rotor with a central opening and, the shutter comprises three blades also forming an opening. The light passes through the central opening of the rotor and through the opening formed by the blades. This figure also shows that a ball bearing is used to maintain the proper positioning between the stator and the rotor. The proper gap between the rotor and stator is critical to allow for proper operation of the motor assembly. Thus, the stator, the ball bearing and the rotor have to be manufactured to high tolerances and carefully assembled with respect to one another. In addition, the rotation of the ball bearing has to overcome its rotational inertia, which requires power, and reduces the amount of torque generated by the motor and affects its uniformity. The assembly of many parts to form a motor in itself increases the motor size and motor complexity. Furthermore, the patent does not describe alignment between the lens barrels and the shutter assembly. As stated above, the precision alignment of the stepper motor to the shutter assembly and the precision alignment of the shutter assembly to the lens barrel assembly is expensive, and may result in an incorrect exposure if the alignment is not performed properly. Finally, the stepper motor and the shutter assembly disclosed in the U.S. Pat. No. 4,005,448 form different and separate parts from the lens barrel assembly. The shutter assembly still needs to be aligned to the lens barrel assembly. The alignment of the shutter assembly to the lens barrel has to be accomplished external to the shutter assembly. The patent does not disclose how this alignment is being done. In addition, the disclosed shutter assembly is large.

U.S. Pat. No. 4,596,449 describes a zoom drive mechanism for moving the lens units (also referred to as lens groups) to varying zoom positions and, therefore, for changing the focal length of the zoom lens system and for the fine focus adjustment. This zoom drive mechanism utilizes a stepper motor comprising a stator and a rotor. The stepper motor elements are mounted to the lens barrels. The rotation of the rotor moves the lens barrels. An improper assembly of the motor to the lens barrels can result in a wrong focal length and degraded image quality. This patent is silent with respect to the issue of aperture/shutter control.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an imaging apparatus that overcomes the problems exhibited by the prior art.

According to one aspect of the present invention, an imaging apparatus includes an annular motor with a central opening and a plurality of lens elements positioned inside the central opening. The motor includes a stator and a homogeneous cylindrical rotor. This rotor is positioned inside the stator and is 0.5 mm to 1.5 mm thick and 2.5 mm to 5 mm long.

According to one embodiment of the present invention the rotor is characterized by an outer cylindrical surface defined by its circumference. The rotor has a plurality of magnetic poles, and the ratio of the circumference of the outer cylindrical surface to the number of magnetic poles is between 1 and 2. According to the embodiment of the present invention the rotor has at least 26 magnetic poles.

The above, and other objects, advantages and novel features of the present invention will become more apparent from the accompanying detailed description thereof when considered in conjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art aperture/shutter system.

FIG. 2 is an exploded view of a directly coupled stepper motor aperture/shutter system of the first embodiment of the present invention.

FIG. 3 is a perspective view of an integral stepper motor housing and a stator assembly.

FIG. 4 is an enlarged view of an integral stepper motor housing and stator assembly.

FIG. 5A is an exploded view of a stepper motor housing, a stator that is being assembled into this housing, a rotor, shutter blades, separators and a cover.

FIG. 5B is an exploded view of a stepper motor housing, a stator that is being assembled into this housing, a rotor, shutter blades, separators and a cover that includes a lens set.

FIG. 6 is a perspective view of a stepper motor housing, stator, rotor, shutter and cover assembly.

FIG. 7 is a cross sectional view of the assembly of FIG. 6.

FIG. 8 is a cut-out view of the assembly of FIGS. 6 and 7 but without the rotor.

FIG. 9 is an exploded view of a directly coupled stepper motor aperture/shutter system of another embodiment of the present invention.

FIG. 10 is a perspective view of the stepper motor housing and stator assembly shown in FIG. 9.

FIG. 11 is an exploded view a zoom lens assembly.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elements forming part of an imaging apparatus in accordance with the present invention. It is understood that elements not specifically shown or described may take various forms well known to those skilled in the art.

FIG. 2 shows the aperture/shutter system of the imaging apparatus of the first embodiment of the present invention. This aperture/shutter system has a plurality of blades that serve as a shutter and that form an aperture that limits the amount of light entering into an lens system (not shown) and, thus, the blades also serve as an aperture stop for the lens system. More specifically, in this embodiment an aperture/shutter system 100 comprises (i) a shutter with a plurality of blades 110, each including a slot 110a, and a hole 110b, (ii) a doughnut like aperture/shutter housing 112 with an internal central hub 112a and (iii) a stepper motor 113 at least partially enclosed by the housing 112. The housing 112 has at least one and preferably more posts 112b in its rear wall 112c (see FIG. 3) for engaging the holes 110b of the blades 110 and providing a pivot support for the blades 110. The blades 110 move, thereby providing a variable aperture opening. A more detailed description of the blades 110 is provided further in the specification. The inner wall 114 of the housing 112 forms a hollow cylinder for providing access to the light propagating along an optical path (through one or more of the lens elements that form the lens system) towards an imaging area 115 on a photosensitive media such as film 116, or an electronic light sensitive device, for example a CCD array (not shown). When one or more lens elements are placed into this hollow cylinder, the length of the lens system (along the optical axis) and the diameters of the lens elements are reduced, because the lens elements are located as close as possible to the aperture stop (formed by the blades 110). The housing 112 may also include hemispherical location pads 114a, a slot 114b and mounting features 112d for a cover 114c. This is illustrated in FIG. 3. The functions of the pads 114a and the slot 114b are described further in the specification.

Referring to FIG. 4, the stepper motor is a magnetic motor that comprises a stator 120 formed with two stator assemblies 120a, 120b. The two stator assemblies 120a, 120b each include a coil 121 of a tightly wound wire and two metal parts 122, 123 surrounding each of the coils 121. (FIG. 4) These metal parts 122, 123 include projections forming teeth 124 that interleave with one another at a close proximity to one another. The teeth 124 act as magnetic poles of the stator 120. More specifically four such interleaved teeth 124 form four poles of the stepper motor 113. The teeth 124 form an inner cylindrical wall 125 of the stator (see FIG. 3).

The stator assemblies 120a, 120b of the stepper motor 113 are located inside the aperture/shutter housing 112, are partially enclosed by this housing and, preferably form an integral part of the aperture/shutter housing 112, for example, by having the plastic aperture/shutter housing 112 molded, extruded, or cast around the stator 120. As used herein, the terms "integral" and "integrally" are defined as being made or formed as a single unit, for example, by casting or molding and does not mean that the pieces are assembled together after their manufacture. For example, in this embodiment, the aperture/shutter housing 112 is not made as a separate piece that is later attached to the stator 120.

More specifically, in this embodiment the metal parts 122, 123 of the stator assemblies 120a, 120b are assembled together and are then encased into the plastic aperture/shutter housing 112 by injection molding the aperture/shutter housing 112 around the stator 120. During the injection molding process, locating pins positioned in the forming apparatus (i.e., a mold) used for injection molding hold the two stator assemblies 120a, 120b in a predetermined location, as the plastic aperture/shutter housing 112 is being molded around these stator assemblies 120a, 120b. Because the aperture/shutter housing 112 is molded around the stator assembly and is integral thereto, the stator 120 provides the required rigidity to the aperture/shutter housing and, the plastic walls of the aperture/shutter housing 112 are made very thin, without compromising the rigidity of the overall aperture/shutter housing 112. Because of this, the aperture/shutter housing 112 is very compact. More specifically, the axial length of the aperture/shutter system and the ratio of the outside diameter d₁ of the aperture/shutter housing 112 to its inner diameter d₂ (see FIG. 2) are very small because the stepper motor 113 is integrated into the aperture/shutter housing 112 and, because the entire aperture/shutter system is symmetrical (with respect to the optical axis defined by the lens elements centered about this axis). It is preferred that the outside diameter d₁ be small (for example, about 28 mm and more preferably 26 mm or less) and that the ratio of an outside diameter of d₁ to the inner preferably 26 mm or less) and that the ratio of an outside diameter of d₁ to the inner diameter d₂ be 2.5≦d₁ /d₂ ≦3.4. It is most preferable that this ratio be 2.7≦d₁ /d₂ ≦3.3. For example, in one implementation, the outside diameter d₁ of the housing 112 of this embodiment is 25 mm and its inner diameter d₂ is 8.0 mm. Therefore, the ratio of an outside diameter of d₁ to the inner diameter is 3.18 and, thus, the annular size Δ=d₁ -d₂ of the aperture/shutter system is very small, i.e., Δ=d₁ -d₂ =8.5 mm. In another implementation, the outside diameter d₁ of the housing 112 is 22 mm and the inner diameter d₂ is 8.0 mm. Therefore, the ratio of an outside diameter of d₁ to the inner diameter is 2.75 and, thus, the annular size Δ is 7 mm. This small annular size is one of the advantages of the present invention. Insert molding plastic housing 112 around the stator 120 further reduces the overall size of the aperture/shutter system since the components do not need to be molded as discreet parts. Since some of the rotor components are eliminated, this results in a very compact aperture/shutter system. In addition, because the rear wall 112c of the aperture/shutter housing 112 is very thin (about 0.4 mm to about 0.9 mm), the lens elements can be located very close to the aperture stop. For manufacturing reasons, it is preferred that the wall thickness be 0.6 to 0.8 mm. In this embodiment it is about 0.7 mm. Although the housing walls are very thin, the rear wall 112c is supported by the stator 120 and, because of this support, it retains its flatness and does not warp, providing proper location for the posts 112b and providing a pivot support for the blades 110.

The stator 120 does not have to be formed integrally with the housing 112, and thus does not have to be insert molded into the housing 112. Instead, the stator 120 can be assembled within the housing 112 using precision assembly. This is shown in a second embodiment of the motor, depicted in FIGS. 5A and 5B (these figures illustrate different covers 114c). However, although such an aperture/shutter system provides some of the size advantages mentioned above, the assembly of housing 112 around the stator 120 has to be done to tight tolerances and this can be difficult and expensive. Also, an additional housing plate with the support posts 112b (for supporting cam pivot points) would be Furthermore, if the aperture/shutter housing is manufactured separately and the stator 120 is then assembled inside the aperture/shutter housing, the walls of the aperture/shutter housing will need to be thicker, in order to provide the required rigidity to the aperture/shutter housing 112, making the aperture/shutter housing 112 larger.

The stepper motor 113 also includes a magnetic rotor 130 (see FIG. 2). The rotor 130 is manufactured as a single, integral part made of the same magnetic material. That is, it is not made of several parts that have been assembled together. The motion of the magnetic rotor 130 is activated by the magnetic fields provided by the stator 120. The rotor 130 of the first embodiment is similar to that of the second embodiment and, is in a form of a ring that has an outer cylindrical surface 130a and an inner cylindrical surface 130b defining a hollow central portion 130c. This hollow central portion 130c provides light access to the imaging area 115. The rotor 130 and the hollow section 130c are centered around the optical axis, and thus are symmetric relative to the optical axis. The rotor 130 is coupled directly (i.e., without any intervening parts, for example, parts made of other materials) to the shutter blades 110 by a plurality of positioning features integrally formed thereon, for example, rotor posts 131. These posts 131 are slidably positioned inside the slots 110a of the shutter blades 110. Thus, there are no intermediate parts, such as a pinion gear and a ring with a sector gear for coupling the rotor to the shutter blades, nor is there a ball barring, such as the one disclosed in U.S. Pat. No. 4,005,448 for positioning the rotor relative to the stator. As the rotor 130 rotates, the blades 110 will pivot about the posts 112b formed on the rear side of the rear wall 112c of the molded housing 112. When the rotor 130 rotates, the blades 110 move as a direct consequence of that rotation. Thus, there is no need for the pinion gear and the ring common to the prior art. Because the rotor 130 is an integral part, and because it couples directly to the shutter blades 110, there is no need for a careful alignment of different parts of the rotor assembly with respect to one another and with respect to the slots 110a of the shutter blades 110. That is, because there are fewer interfaces among the different parts, there are fewer tolerances that may add together. This decreases the cost of the aperture/shutter system and improves it accuracy.

The rotor 130 is magnetic and is made of a moldable material that is capable of being magnetized, for example, an isotropic neodymium-iron-boron, an isotropic samarium-cobalt, praseodymium-iron-boron, or other rear earth magnetic material. After the rotor 130 is molded it is magnetized to form a plurality of magnetic poles thereon. The larger the number of poles, the more aperture settings are feasible. An imaging system with multiple aperture settings (corresponding to multiple F-numbers) require that a motor has at least that number of steps plus two more steps in order to completely close the aperture opening. Thus, if seven aperture sizes are required (corresponding to seven F-number values) of the lens system, then a minimum of nine steps are required of the motor. These steps correspond to the seven aperture settings and two steps for the home position (to completely close the shutter blades). However, it is preferred that the number of magnetic poles be 20 or more, and even more preferred that it be at least 26 and most preferable over 30 poles. It is difficult to produce more than 50 poles in the rotor of this size because of the high coercivity of the material forming the rotor. However, a rotor with a larger circumference may have a larger number of poles. The closer the poles are with respect to one another (around the outer circumference of the rotor) the less rotation is required of the rotor and the faster is the shutter response to open and close control sequences. In this embodiment the lens system has seven aperture sizes and the outer cylindrical surface 130a of the magnetic rotor 130 has thirty six equidistant magnetic poles (18 north poles and 18 south poles) facing the stator. The north poles are sandwiched between the south poles and the south poles are sandwiched between the north poles of the rotor. The diameter of an inner cylindrical surface 130b of the rotor 130 is 13.58 mm and diameter of the outer cylindrical surface 130a of the rotor 130 is about 16.3 mm. The circumference of the outer cylindrical surface 130a is 51.2 mm. It is preferred that the pole density D_(p) of the rotor (defined as the ratio of the circumference of the outer cylindrical surface 130a to the number of magnetic poles) be less than 2. It is more preferable that the pole density be 1≦D_(p) ≦1.7. It is even more preferable that the pole density be 1.1≦D_(p) ≦1.7. It is most preferable that the pole density be 1.28≦D_(p) ≦1.7. In this embodiment, the pole density D_(p) =51.2/36≈1.4. That is, the centers of the adjacent magnetic poles are approximately 1.4 millimeter apart.

In this embodiment, in order to reduce the mass of the rotor, the rotor 130 is positioned inside the stator 120. However, the position of the rotor and the stator may be reversed--i.e., the stator may also be positioned inside the rotor. In order to keep the motor compact it is preferable that the rotor be as small as possible while its hollow section 130c be as large as possible (in order to increase the F-number of the lens system). Thus, it is preferred that the thickness of the rotor be about 1.5 mm or less, and that its length (without the posts) be less than 5 mm. The small size of the rotor makes it light and easy to turn, providing a higher torque. However, if the rotor is too small, it does not generate enough magnetic field and that makes it difficult to rotate. Therefore it is preferred that (i) the rotor thickness be about 0.5 mm to about 1.5 mm and (ii) the rotor length be 2.5 to 5 mm, and preferably 3 to 4 mm. In this embodiment the thickness of the rotor 130 is about 1 mm and the length of the rotor is about 3.5 mm long. The rotor posts are molded together with the rotor and are integral therewith. These posts are approximately 2 mm long and their diameter is about 1 mm.

The rotor 130 is kept in proper position with the internal central hub 112a, hemispherical location pads 114a and the cover 114c. Although the rotor 130 rotates, the hub 112a does not. The hub surface engages the inner cylindrical surface 130b of the rotor 112 and rotably supports the rotor 112. Because there is no rotational inertia associated with the movement of the hub, the motor requires less power and the torque generated by the motor is greater and is more uniform than the torque generated by the prior art motors such as the one disclosed in U.S. Pat. No. 4,005,448. The rotor 130 also includes a horizontally extending key 132. The slot 114b of the molded housing 112 is used to engage the key tab 132 of the rotor 130 to constrain its range of rotation from aperture closed position to full open position. Features molded into the aperture/shutter housing 112 include the internal central hub 112a which supports the rotor 130 and which determines the position of the inside diameter of the rotor 130, and a slot 114b which holds a key tab 132 (from the rotor 130) inserted into it. This slot 114b limits the travel of the rotor in both directions. The total amount of rotation for the rotor 130 of this embodiment is ±25 degrees. The full rotation of the rotor 130 is performed in ten 5 degree steps.

The hub 112a of the aperture/shutter housing 112 determines the position of the rotor 130, and if the position of the stator 120 deviates too much from the specified position (due to build up of manufacturing and assembly tolerances), the rotor 130 may contact the stator 120, causing the motor 113 to stall. Thus, in order to improve the accuracy of the features in the aperture/shutter housing 112 that position the rotor 130 with respect to the stator 120, it is preferred to integrally form the aperture/shutter housing 112 and a stator 120 rather than to assemble them together. This can be accomplished, for example, by insert molding the aperture/shutter housing 112 around the two stator assemblies 120a, 120b as described in the first embodiment. This eliminates the positional variation exhibited by the prior art aperture/shutter assemblies due to assembly of separate parts of the aperture/shutter housing 112 and the rotor 130 and stator 120 with respect to one another. Because insert molding the stator 120 inside the aperture/shutter housing 112 (as it was done in the first embodiment) allows additional precision in positioning of the rotor 130 with respect to the stator 120, this in turn allows the gap d₃ (FIG. 2) between the stator 120 and the rotor 130 to be reduced. This gap d₃ is formed as follows. The outer cylindrical surface 130a of the rotor 130 is of a smaller diameter than the inside surface 125a of the inner cylindrical wall 125 of the stator 120. The inner cylindrical surface 130b of the rotor 130 sits on the cylindrical hub 112a of the aperture/shutter housing 112. Therefore, an annular gap d₃ is formed between the inside surface 125a of the inner cylindrical wall 125 of the stator 120 and the outer cylindrical surface 130a of the rotor 130. The size of the gap d₃ is one of the primary factors in determining the available torque of the motor. Therefore, as the gap d₃ between the stator 120 and the rotor 130 is reduced, the torque is increased and this results determining the available torque of the motor. Therefore, as the gap d₃ between the stator 120 and the rotor 130 is reduced, the torque is increased and this results in faster acceleration of assembly and therefore faster shutter time. The reduction in gap distance also results in less need for power to drive the motor (i.e., lower voltage or less current) in order to achieve the same performance (rotational speed of the rotor).

The aperture stop/shutter shown in FIGS. 2 and 5A includes at least three shutter blades 110, which also function as the aperture setting blades. It is noted that either a larger or a smaller number of shutter blades may also be used. As discussed above, each of the shutter blades 110 includes a cam slot 110a for engaging a corresponding feature, such as posts 131 situated on the rotor 130. The shape of these cam slots 110a determines the size of the apertures. The shutter blades 110 also include a plurality of holes 110b for engaging the posts 112b located on the rear wall 112c of the aperture/shutter housing 112 (FIG. 3), or for engaging posts 112B of a rear plate 112c' (FIG. 5A). In the first embodiment, the posts 112b are molded with the aperture/shutter housing 112 and are integral with the aperture/shutter housing. The positioning precision of these posts 112b are an important factor that effects the accuracy of the aperture opening. Since posts 112b are formed integrally with the aperture/shutter housing, their position is always accurate. Thus, molding the posts 112b with the rest of the aperture/shutter housing increases the accuracy of the aperture/shutter system 100 and eliminates the expense of complex alignment during assembly.

Two separators 140a and 140b provide a smooth surface for the shutter blades 110 to slide on. An upper separator (140a) is used to hold the shutter blades 110 in a plane and to reduce the oscillating movement of the shutter blades 110 and the rotor 130 when motor 113 is stopped at the desired aperture. The lower separator 140b is used for setting the maximum aperture opening and has a smaller central hole 140b' than the hole 140a' of the housing or of upper separator 140a. The cover 114c is used to hold the rotor 130, shutter blades 110, lower separator 140a, and upper separator 140b in place. This cover 114c attaches to the housing 112 with screws, heat stake posts 112d or a snap (not shown) (See FIGS. 6, 7, and 8.) The cover 114c includes a plurality of features, for example, holes 114d (see, for example, FIGS. 2, 5A, 5B) that engage complimentary features, such as heat stake posts 112d formed on the rear wall 112c of the housing 112. The cover 114c also functions as a lens mount and, therefore, may include at least one integrally molded lens seat 114c'. This is shown in FIG. 5B. As mentioned earlier, the stepper motor 113 comprises a doughnut like housing 112 encasing two stator assemblies 120a, 120b and a rotor 130, at least partially encased in the housing 112. The molded aperture/shutter housing 112 also includes the heat stake posts 112d or holes 112d' (see FIG. 4) for the screws in order to allow attachment of the cover 114c to the housing 112. This configuration also results in an aperture/shutter system with an annular shape of a smaller size and a greater aperture opening (which is especially suitable for zoom lens systems) and in fewer parts to assemble, thereby reducing the cost of the aperture/shutter assembly.

The aperture/shutter system of the imaging apparatus may also have the housing 112 which serves as a lens barrel. This is shown in FIGS. 8, 9 and 10. More specifically, the shutter/aperture system 100 of the imaging apparatus can also include one or more lens mounts 150 with lens seats 151 for holding one or more lens elements. The lens mounts, including the lens seats 151, are formed integrally with the housing 112 and the stator 120 for example, by plastic molding or casting. Thus, according to this embodiment, the aperture/shutter system 100 of the imaging apparatus incorporates the integral housing 112, the rotor 130, the shutter components and an integrally formed, for example by plastic molding, lens seat 151 and the stator 120. More specifically, the metal stator 120 is assembled first and the aperture/shutter housing 112 with lens seats is molded around the stator 120. With reference to FIG. 9, the lens mounts 150 may include a lens element locating and retaining feature, such as the ring 152 and a lens seat 151 for one or more lens elements. In addition, the housing 112 may also include an integral axially extended ring 153 that can be heated and pressed against a lens element situated adjacent to it, forming a heat seal and retaining the lens

The embodiment of the aperture/shutter housing 112 with the lens mounts 150 may also have features that could mate to a lens barrel that contains the lens elements of the imaging apparatus. For example, FIGS. 9 and 10 show that the housing 112 has a helictical thread 155 formed on its external surface. The helictical thread 155 interacts with a complimentary thread of a lens barrel or a sleeve, allowing the housing 112 to be assembled inside the lens barrel or inside the sleeve. Furthermore, another, smaller lens barrel may be slidably positioned inside the housing 112. This smaller lens barrel engages a rib 157 of the housing 112, so that the smaller barrel can slide along the rib 157 without rotating relative to the housing 112. Other features for engaging lens barrels or other mechanisms may be also molded on the housing 112.

FIG. 11 illustrates a zoom lens assembly of the imaging apparatus of another embodiment of the present invention. This zoom lens assembly comprises an aperture/shutter assembly (with or without lens elements situated in its hollow portion) and at least one lens barrel mated to the aperture/shutter assembly. A zoom lens assembly includes a plurality of lens groups (each containing one or more lens elements), at least one of which is movable in order to provide a zoom lens system with the desired zoom ratio. The lens elements, in combination, form images of photographed objects on a photosensitive medium such as film, or a CCD array.

More specifically, FIG. 11 shows a smaller lens barrel 160 with positioning features 161 for engaging a plurality of ribs 157 of an aperture/shutter system 100. These ribs 157 prevent the rotation of the smaller lens barrel 160 within the aperture shutter housing 112. This lens barrel 160 fits within the aperture shutter housing 112. The aperture/shutter system 100 includes an integral housing 112, with a stator 120 and lens mounts which include lens seats 151 for holding two lens elements 170. FIG. 11 also shows a rotor 130, and a plurality of shutter blades 110 sandwiched between two separators 140a and 140b. The whole assembly fits inside the housing 112 and is enclosed inside the housing 112 by a rear cover 114c. The small lens barrel 160 provides support for lens elements 171, 172 and is slidably fitted inside the housing 112. In addition, a rear lens barrel 173 supports a lens element 174 and also fits inside the housing 112.

The following are some of the advantages of the aperture/shutter system of the present invention:

The imaging apparatus includes aperture/shutter system that has a small size, large central opening and fewer parts to assemble, thereby reducing the cost of the imaging apparatus.

It is an advantage that the imaging apparatus includes a small motor which contains a large number or closely spaced magnetic poles, thus allowing fast shutter response and very quick changes from one aperture setting to another aperture setting. Zoom lens systems require many different aperture settings, because as zoom lens system changes its focal length (from wide to telephoto, for example) the aperture size changes. The larger the zoom ratio, the greater is the number of different aperture settings required. Thus, this invention is especially suitable to zoom lens systems and is even more suitable to zoom lens systems with large zoom ratio (2× or higher).

The term "aperture/shutter system" defines a device that can be operated either as (i) a light controlling aperture only (in which case a camera may or may not require an additional shutter activated by an additional motor or other means; or (ii) a shutter having only an open and closed position; or (iii) a combination aperture shutter system that operates both as a light controlling aperture and a shutter.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

PARTS LIST

100 aperture/shutter system

110 blades

110a slot

110b hole

112 aperture/shutter housing

112a internal central hub

112b post

112c rear wall

112d stake posts

112d' holes

113 stepper motor

114 inner wall

114a hemispherical location pads

114b slot

114c rear cover

114d holes

115 imaging area

116 film

120 stator

120a, 120b stator assemblies

121 coil

122, 123 metal parts of the stator assembly

124 interleaved teeth

125 cylindrical wall

125a inside surface

130 rotor

130a outer cylindrical surface

130b inner cylindrical surface

130c hollow central portion

131 post

132 key tab

140a upper separator

140a' upper separator central hole

140b lower separator

140b' lower separator central hole

150 lens mount

151 lens seat

152 ring

153 extended ring

155 helictical thread

157 rib

160 small lens barrel

171, 172 lens elements

173 rear lens cell

174 rear lens element 

What is claimed is:
 1. An imaging apparatus comprising:an annular motor with a central opening, said motor including a stator and a homogeneous cylindrical rotor, said rotor being positioned inside said stator, said rotor being 0.5 mm to 1.5 mm thick and 2.5 mm to 5 mm long; and a plurality of lens elements positioned inside said central opening.
 2. An imaging apparatus according to claim 1 wherein said rotor is 3 mm to 4 mm long.
 3. An imaging apparatus according to claim 1 wherein said rotor is made of neodymium-iron-boron.
 4. An imaging apparatus according to claim 3 wherein said rotor has 36 poles.
 5. An imaging apparatus according to claim 3 wherein said rotor has at least one integral positioning feature coupled to another part of said imaging apparatus.
 6. An imaging apparatus according to claim 5 wherein integral positioning feature is a post and said another part is at least one shutter blade.
 7. An imaging apparatus according to claim 1 wherein said rotor has at least 26 magnetic poles.
 8. An imaging apparatus according to claim 1 wherein said rotor has 36 magnetic poles.
 9. An imaging apparatus according to claim 1 wherein said rotor a plurality of magnetic poles and the centers of adjacent magnetic poles are 1 mm to 1.7 mm apart.
 10. An imaging apparatus according to claim 1 wherein said rotor a plurality of magnetic poles and the pole density is less than
 2. 11. An imaging apparatus according to claim 1 wherein said rotor is characterized by an outer cylindrical surface, said surface being defined by its circumference, said rotor having a plurality of magnetic poles, and the ratio of the circumference of the outer cylindrical surface to the pole number is between 1 and
 2. 12. An imaging apparatus according to claim 10 wherein said ratio of the circumference of the outer cylindrical surface to the pole number is between 1.28 and 1.7.
 13. An imaging apparatus according to claim 1 wherein said rotor has at least 26 magnetic poles and at least one integral positioning feature coupled to another part of said imaging apparatus.
 14. An imaging apparatus according to claim 13 wherein integral positioning feature is a post and said another part is at least one shutter blade.
 15. An imaging apparatus according to claim 14 wherein said post is 1 mm to 2 mm long.
 16. An imaging apparatus defining an optical path, said imaging apparatus comprising:a shutter mechanism operable at a first state to selectively block light along said optical path and a second state to allow light along said optical path; an annular motor with a central opening, said rotor including a stator and a homogeneous cylindrical rotor, said rotor being positioned inside said stator, said rotor being 0.5 to 1.5 mm thick and 2.5 to 5 mm long, said rotor being coupled to said shutter mechanism to move said shutter mechanism between said first and said second state; and a plurality of lens elements positioned inside said central opening.
 17. An imaging apparatus according to claim 16 wherein said rotor is 3 mm to 4 mm long.
 18. An imaging apparatus according to claim 16 wherein said rotor a plurality of poles and the centers of adjacent poles are less than 2 millimeters apart.
 19. An imaging apparatus comprising:a plurality of lens elements forming an image on a photosensitive medium; an annular motor with a central opening operatively connected to said plurality of lens elements, said motor including a stator and a homogeneous cylindrical rotor, said rotor being positioned inside said stator, said rotor having a plurality of magnetic poles and the centers of adjacent magnetic poles are 1 mm to 1.7 mm apart.
 20. An imaging apparatus according to claim 19 wherein at least one of said plurality of lens elements is positioned inside said central opening.
 21. An imaging apparatus according to claim 19 further comprising a shutter mechanism operable at a first state to selectively block light along said optical path and a second state to allow light along said optical path; and wherein said rotor is coupled to said shutter mechanism to move said shutter mechanism between said first and said second state. 